1. Field
Aspects relate to an image forming apparatus and a low power driving method thereof.
2. Description of the Related Art
A low power mode is a mode in which the power supply to most of the modules is shut down or minimized so as to minimize power consumption when a system is inactive. In order to implement lower standby power, the power supply may be shut down to main memory (in general, external dynamic random access memory (DRAM)), or the main memory may enter self refresh state and internal memory (in general, internal static random access memory (SRAM)) which is not in use in system on chip (SOC) drives a program. SRAM usually uses small quantity of memory of approximately 128 kilobytes.
However, as in a Universal Serial Bus (USB) driver for printers or large-capacity storage devices, if bulk data transmission is required or the number of supportable interfaces is increased, space taken up by a stack is increased, so it is difficult to implement all functions of the USB driver in a small-capacity SRAM.
In addition, it is inefficient to apply large-capacity SRAM of a high cost.
If a device which is used as a USB device cuts off the power supply to the external DRAM so as to enter the low power mode, a USB driver in the external DRAM also stops its operation, so the device cannot communicate with a USB and a host device. In particular, if the host device, for example, a personal computer (PC) sends a specific operation command, for example, a printing command to the device through the USB, the host device cannot perform the command (that is, the PC recognizes that connection with the device is cut.). Accordingly, in a related art, the external DRAM should operate normally in the low power mode.
If power is continuously supplied to the external DRAM, standby power is consumed. To consume lower power, if the power supply is cut off to the external DRAM, the USB driver does not operate, so communication through the USB may be impossible. In this case, if a program which monitors the state of the device using the USB approaches, it is determined that the device is turned off, thereby causing inconvenience. For example, if the PC is connected to the printer through the USB and has a printer monitoring program, when the DRAM of the printer is turned off and the USB driver does not operate, the PC may recognize that the printer is in an abnormal state or connection with the printer is cut off.
Therefore, there is a need for a low power driving method of an image forming apparatus.